TheScouring of Nebulos was the final battle of theGreat War, a destructive conflict that embroiled the planetNebulos and ultimately left the planet devastated and incapable of supporting life.

Fiction

Beast Wars: Uprising

The Scouring of Nebulos began with theDecepticon's initial destabilization of the planet in the 21st century. Their agent, a 'con namedZarak, used the Decepticoninfiltration protocol to spark a war between the planet'sHive nations at war with theWorld Watcher alliance. Just as this started however, theHuman Confederacy showed up. With their arrival, the war turned hot. The Decepticons quickly forged an alliance with the Hive, their technologies meshing pretty well. Captive Autobots and World Watchers were experimented on by the madFausto Borx in hideous fashions, from which theHeadmaster technology was born.

Not to be outdone, the Autobots managed to create Headmasters of their own. Soon enough, the team ofTeslor andArcana managed to expand the process to includeTargetmasters as well, giving the Autobots the upper-hand in the already destructive conflict... until the NebulonsFracas andNightstick defected to the Hive.

In2031, Fausto and Zarak, already bonded together, turned the city ofKinodia into the gargantuanMegaZarak, the first double-Headmaster. The Autobots retaliated by transformingCerebros andSpike Witwicky intoFortress Maximus—an awesomely powerful cityformer that took thousands of lives during the course of the Nebulos campaign.A Brush With Infamy–PrologueHead Games

Fortress Maximus and MegaZarak fought, their battle laying waste to what was left of Nebulos, destroying mountains and seas alike. It concluded when the Autobots used Fausto's daughterLlyra as a distraction, allowing Fortress Maximus to win. But the damage was already done. Nebulos had been rendered completely lifeless and would never again support life.A Brush With Infamy–Prologue

The destruction that Fortress and his fellow cityformer wrought proved to be the final straw for the Human Confederacy and its allies, who decided that the Cybertronian civil war was over and forcibly imposed an armistice on both factions. Fortress Maximus and the other Cybertronians responsible for the devastation were subsequently exiled back toCybertron's newAllowed Zone and forbidden from leaving.Head GamesMicro-Aggressions